Low-residual lithium battery positive tab adhesive material and preparation method thereof

Abstract

The application discloses a low-residual lithium battery positive electrode tab adhesive material and a preparation method thereof, and belongs to the technical field of lithium battery auxiliary materials. The preparation method comprises the steps of copolymer synthesis, premixing, filler dispersion, cross-linking system introduction and defoaming, coating and packaging. The copolymer is prepared by radical copolymerization of norbornene, hexafluorobutyl acrylate and maleic anhydride, and the fluorinated hyperbranched polyester is functionalized by ester exchange and epoxy ring opening in one step. The application is aimed at the problems of high high-temperature residue, weak interfacial adhesion and poor electrolyte resistance of the existing adhesive. By designing the fluorine-containing copolymer with high thermal stability and high reactivity as the main body, cooperating with the reaction-type compatibilizer to build a strong chemical bonding interface, and introducing the hyperbranched stabilizer with the functions of physical binding and chemical chelation, the tab adhesive material with ultra-low residue, ultra-high peel strength and excellent electrolyte resistance is successfully prepared, which can meet the long-term reliable sealing requirements of high-energy-density lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery auxiliary materials technology, and in particular to a low-residue lithium battery positive electrode tab adhesive film bonding material and its preparation method. Background Technology

[0002] As a core energy storage device in the new energy field, the safety and cycle life of lithium batteries depend on the bonding reliability of the positive electrode tab, current collector, and separator. The positive electrode tab adhesive film, as a key auxiliary material, directly affects the interfacial bonding stability and service safety, and has become a focus of industry research and development. Currently, most tab adhesive films are based on epoxy resin and ordinary acrylate, which must meet the stringent requirements of high-temperature cycling and electrolyte immersion.

[0003] Existing adhesive materials have three major defects: First, high residual amount after high temperature (above 120℃) cycling, traditional resin molecular chains are prone to carbonization and accumulation, resulting in a surge in electrode contact resistance and reduced charge and discharge efficiency; second, insufficient interfacial bonding stability, poor compatibility between the main resin and aluminum foil current collector and positive electrode active material, and easy interfacial peeling after long-term use; third, lack of migration resistance and electrolyte resistance, small molecule additives are prone to migration, leading to film performance degradation, and the adhesion strength retention rate after electrolyte immersion is often less than 70%.

[0004] To address these issues, existing technologies often employ methods such as optimizing the crosslinking agent ratio or improving coating precision. For instance, increasing the amount of curing agent can increase crosslinking density, but this can easily lead to film embrittlement. Alternatively, a single silane coupling agent can be used to improve interfacial compatibility, but this cannot simultaneously solve the problems of residue and anti-migration. Existing solutions do not construct a synergistic system based on the molecular structure design of materials, making it difficult to achieve low residue, high adhesion, and anti-migration performance, and thus failing to meet the stringent requirements of high-energy-density lithium batteries for electrode tab adhesive materials. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a low-residue lithium battery positive electrode tab adhesive film bonding material and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a low-residue lithium battery positive electrode tab adhesive film includes the following steps:

[0008] S1. Preparation of fluorinated cyclic olefin-maleic anhydride copolymer:

[0009] Under dry nitrogen protection, norbornene, hexafluorobutyl acrylate and maleic anhydride and dehydrated toluene were added to a reaction vessel, heated to 85°C, benzoyl peroxide was added, and the reaction was carried out for 6 hours. The mixture was poured into an ethanol / water mixed solvent, filtered, washed with ethanol, and dried to obtain a fluorinated cyclic olefin-maleic anhydride copolymer.

[0010] At 85℃, benzoyl peroxide (BPO) in the system undergoes thermal decomposition, and the peroxy bond (-OO-) in its molecule breaks to generate benzoyloxy free radicals, which provide highly active initiation centers for subsequent polymerization. At this temperature, BPO has moderate decomposition efficiency, which can avoid the problems of uneven molecular chain distribution caused by too fast initiation or incomplete reaction caused by too slow initiation.

[0011]

[0012] The growth stage is the core of copolymer chain formation. Benzoyloxy radicals first attack the C=C double bonds of norbornene, hexafluorobutyl acrylate, or maleic anhydride to form primary monomer radicals. Subsequently, based on the complementary electronic properties of the three monomers, they continuously and alternately add to each other. The electron-withdrawing properties of maleic anhydride and the electron-donating properties of norbornene and hexafluorobutyl acrylate promote each other, so that the three monomers are uniformly embedded in the molecular chain, avoiding homopolymerization or local aggregation of single monomers, and finally forming a ternary random copolymer molecular chain. The termination stage is completed by free radical coupling. When the molecular chain grows to the set length, two active polymer radicals collide and couple to form a stable copolymer molecule. No small molecule byproducts are generated in this process, reducing the risk of residual film in the subsequent process from the source.

[0013]

[0014] In this system, norbornene provides a highly rigid cyclic olefin backbone, endowing the copolymer with excellent high-temperature resistance and mechanical stability. The steric hindrance of its cyclic structure can also suppress the thermal motion of the molecular chain and reduce the tendency for high-temperature carbonization. Hexafluorobutyl acrylate introduces 7-9 wt% fluorine, which enhances electrolyte resistance due to the strong electronegativity and hydrophobicity of fluorine atoms. Maleic anhydride introduces 10-13 mol% of highly reactive anhydride groups. The five-membered ring of maleic anhydride is a highly strained five-membered ring, which is easy to open under high temperature, strong nucleophiles (such as amines, alcohols, and water), or ionic initiators. It does not participate in free radical polymerization and provides sites for subsequent reactions with compatibilizer hydroxyl groups and photocrosslinker epoxy groups. Dehydrated toluene, as a good solvent, ensures homogeneous mixing of all components. Dehydration treatment can prevent the hydrolysis of hexafluorobutyl acrylate to generate hydrofluoric acid. Ethanol / water mixed solvent, as a precipitant, can quickly precipitate the copolymer and wash away unreacted monomers, improving product purity and laying the foundation for the low residue characteristics of the film.

[0015] S2. Preparation of hyperbranched polyesters with fluorinated alkane-modified end groups:

[0016] Under nitrogen protection, hydroxyl-terminated hyperbranched polyester and N,N-dimethylformamide were added to a reaction vessel, stirred and dissolved, heated to 80°C, and ethyl acetoacetate was slowly added dropwise. The reaction was carried out for 7 hours, then perfluorooctyl propylene oxide and tetrabutylammonium bromide were added, and the reaction was continued at 70-75°C for 10 hours. The product was precipitated with ice-cold ether, filtered, washed three times with ethanol, and dried under vacuum for 12 hours to obtain a hyperbranched polyester product with fluoroalkane-modified terminal groups.

[0017] After the hydroxyl-terminated hyperbranched polyester is dissolved in N,N-dimethylformamide, at 80℃, the ester groups of ethyl acetoacetate and the hydroxyl groups of the hydroxyl-terminated hyperbranched polyester exchange under thermal drive, forming ester bonds and releasing ethanol, so that the end groups of the hyperbranched polyester are grafted with ethyl acetoacetate groups, and further transformed into β-diketone structures. The reaction at 7h ensures that the end group modification rate is ≥90%. This structure provides active sites for subsequent metal chelation and is the core of the anti-migration function.

[0018]

[0019] Tetrabutylammonium bromide, as a phase transfer catalyst, solves the problem of interfacial reaction between hydrophobic perfluorooctyl propylene oxide and hydrophilic hyperbranched polyester. At 70-75℃, the epoxy groups of perfluorooctyl propylene oxide are nucleophilically attacked by the residual terminal hydroxyl groups of hyperbranched polyester, resulting in a ring-opening reaction. Fluorine-containing segments are grafted to the molecular ends via ether bonds. The fluorine content reaches 3-5 wt% in 10 hours. The fluorine-containing end groups can improve the compatibility with the main fluorine-containing system and enhance the resistance to electrolytes.

[0020]

[0021] The three-dimensional hyperbranched structure in hyperbranched polyesters with fluorinated alkanes at the end groups can confine small molecule migrations within the polymer matrix through physical steric hindrance, and its high-density β-diketone groups on the surface act as potent bidentate ligands, actively capturing trace amounts of Al dissolved from aluminum tabs. 3+ Fe 3+ Metal ions form stable five-membered ring chelates, completely eliminating the catalytic oxidation effect of these ions on the polymer chain;

[0022] The outer perfluorooctyl segment is highly compatible with the fluoropolymers in the system through fluorine-fluorine interactions, ensuring that the stabilizer is uniformly dispersed and exists stably in the interfacial region for a long time. At the same time, its strong hydrophobic and oleophobic properties form a secondary barrier against electrolyte penetration. This design, through the synergy of "physical binding - chemical chelation - interfacial compatibility", fundamentally inhibits the generation and accumulation of interfacial degradation products under high temperature cycling and electrolyte immersion. It is a key functional component for achieving ultra-low residue and long life durability of adhesives.

[0023] S3. Premixing:

[0024] Fluorinated cyclic olefin-maleic anhydride copolymer, hydroxyl-terminated fluorinated polyether and trimethylolpropane triacrylate were added to a planetary mixer and stirred for 60 min at 60 °C and a vacuum of -0.095 MPa to obtain a uniform, transparent or semi-transparent viscous premixed melt.

[0025] Under 60°C and vacuum conditions, the molecular chain mobility of the main polymer, the fluorinated cyclic olefin-maleic anhydride copolymer, is enhanced. Its rigid skeleton gradually swells and disperses in the reactive diluent trimethylolpropane triacrylate. Trimethylolpropane triacrylate, as a low-viscosity reactive solvent, penetrates and encapsulates the copolymer segments, significantly reducing the viscosity of the system. At the same time, the fluorinated polyether with terminal hydroxyl groups, with its fluorinated segments similar to those of the copolymer, achieves excellent thermodynamic compatibility through fluorine-fluorine interactions and is uniformly dispersed in the system. Vacuum conditions effectively remove trace amounts of moisture and air adsorbed by the raw materials, avoiding moisture interference with subsequent reactions.

[0026] The anhydride five-membered ring of the copolymer side chain can undergo a preliminary esterification ring-opening reaction with the hydroxyl group at the end of the hydroxyl-terminated fluorinated polyether. This reaction first involves the nucleophilic attack of the hydroxyl group on a carbonyl carbon of the anhydride, leading to the ring opening of the anhydride ring and the formation of an ester bond and a free carboxyl group. This establishes a key chemical bond between the copolymer and the hydroxyl-terminated fluorinated polyether, thereby anchoring the compatibilizer to the polymer backbone in a covalent manner and fundamentally preventing subsequent phase separation. The ether bond (-O-) and fluorinated segments in the compatibilizer molecular chain have lone pair electrons and low surface energy. During subsequent use, they can generate strong physical adsorption and interaction with the alumina on the aluminum tab surface through coordination bonds, hydrogen bonds and van der Waals forces, achieving a strong and stable interfacial bond.

[0027] The 60℃ temperature setting is a key process parameter. This temperature is lower than the glass transition temperature of each component, avoiding thermal degradation of the components. At the same time, it can significantly reduce the melt viscosity of the copolymer, weaken the internal friction between molecular chains, and provide kinetic energy for the penetration of reactive diluents and the dispersion of solubilizers. The vacuum environment of -0.095MPa can remove residual trace amounts of air and low-boiling-point volatiles in the system in real time, avoiding film defects caused by air bubbles during subsequent curing. The 60min stirring and mixing process uses the combined revolution and rotation of the planetary mixer to form three-dimensional shear force, which gradually depolymerizes the micron-sized aggregates of the copolymer, allowing the solubilizer and reactive diluent to uniformly coat its molecular chains, ultimately forming a transparent or semi-transparent viscous premixed melt. Transparency is a direct characterization of the molecular-level dispersion of components, indicating the absence of macroscopic phase separation, laying the foundation for the uniformity of subsequent filler dispersion and crosslinking reaction.

[0028] After the materials are mixed, the fluorinated cyclic olefin-maleic anhydride copolymer serves as the main skeleton, providing initial melt structure support; the hydroxyl-terminated fluorinated polyether is pre-dispersed with the main body through the compatibility of the fluorinated segments, reserving uniformly distributed hydroxyl sites for subsequent reactions with anhydride groups; trimethylolpropane triacrylate acts as an active diluent to reduce the viscosity of the system, while its acrylate groups reserve active sites for subsequent photocrosslinking reactions. The three achieve pre-synergistic effects of "structure-activity-processability" through physical interactions.

[0029] S4. Packing dispersion:

[0030] Modified nano-zirconia, hyperbranched polyester with fluoroalkane-modified end groups, and polyether-modified polydimethylsiloxane were added sequentially to the premixed melt. The mixture was then stirred and dispersed at low speed for 15 min under 60℃ and -0.095MPa vacuum conditions, followed by high-speed dispersion for 40 min.

[0031] Under mild heating at 60℃ and continuous vacuum, the viscosity of the premixed melt is further reduced and its fluidity is enhanced. The methacrylate groups (-COOCH=CH2) grafted onto the surface of the modified nano-zirconia have excellent chemical similarity with the acrylate components such as reactive diluents and photocrosslinking agents in the melt. Following the principle of "like dissolves like," the polymer chain segments can effectively wet and coat the surface of the nanoparticles, overcoming their tendency to agglomerate due to high surface energy. The low-speed stirring stage mainly achieves macroscopic wetting and initial deagglomeration of the filler, breaking up large aggregates. Subsequently, high-speed shearing provides strong hydrodynamic forces, further breaking up micron-sized agglomerates and ensuring that individual nanoparticles are fully wrapped by the polymer melt, achieving nanoscale dispersion.

[0032] In this process, the hyperbranched polyester with fluorinated alkane-modified end groups plays a key role. Its fluorinated alkane end groups generate strong fluorine-fluorine hydrophobic interactions with the fluorinated polymer segments in the system, allowing it to be uniformly distributed in the matrix. Its hyperbranched three-dimensional spherical structure forms a "soft wrapping" of nanoparticles in physical space, preventing them from getting close to each other and playing a role in steric stabilization. More importantly, the β-diketone chelating groups on the periphery of its molecules can form coordination bonds with zirconium ions on the surface of nano-zirconia that are not completely covered by silane coupling agents, achieving chemical anchoring. This dual effect of "physical wrapping + chemical anchoring" gives the nanofiller irreversible dispersion stability.

[0033] Polyether-modified polydimethylsiloxane serves as a highly efficient dispersant and surface control agent. Its polyether segments are hydrophilic and anchored to the polar groups of fillers or polymers, while its siloxane segments are hydrophobic and oleophobic, extending into the polymer matrix. By adsorbing at the filler-polymer interface, it significantly reduces interfacial tension, promotes wetting, and forms a lubricating molecular layer, reducing friction between the filler and polymer chains. This results in more efficient dispersion under the same shear force, ultimately yielding a slurry with lower viscosity and better leveling properties. The vacuum environment continuously eliminates air that may be entrained by high-speed stirring, ensuring a dense and defect-free slurry.

[0034] This dispersion step is the core process for constructing high-performance nanocomposite adhesives. The uniformly dispersed modified nano-zirconia, as a rigid structure, acts as stress support points and crack pinning points in the crosslinked network formed during subsequent curing, which can significantly improve the tensile strength, modulus, and heat resistance of the adhesive film. The introduction of hyperbranched polyester with fluoroalkane-modified end groups not only stabilizes the filler, but its own hyperbranched structure also plays an internal plasticizing role, improving the toughness of the adhesive film. At the same time, its metal chelating ability provides a guarantee for long-term inhibition of interfacial catalytic degradation. The addition of dispersant ensures the excellent workability of the slurry, which is a prerequisite for obtaining a uniform thickness and defect-free adhesive film. The slurry finally formed in the whole process needs to achieve a particle size D90≤50nm, which indicates that the filler has achieved an ideal nano-dispersion state, laying the foundation for the uniformity and reliability of the final adhesive film performance.

[0035] S5. Introduction and degassing of the crosslinking system:

[0036] The mixture was cooled to 35°C, and epoxy acrylate and photoinitiator were added under light-protected conditions. The mixture was stirred for 25 minutes and then allowed to stand under a high vacuum of -0.098MPa for 30 minutes to degas, thus obtaining the final adhesive slurry.

[0037] This step is the final construction and slurry purification process of the photocurable crosslinking system. Its core mechanism is the physical mixing and dissolution equilibrium of photoactive components and the physical removal of microbubbles. It may also be accompanied by a very preliminary photoinitiator activation pre-reaction, which prepares the final conditions for rapid deep curing under ultraviolet (UV) irradiation.

[0038] Lowering the system temperature from 60°C to 35°C is a key process control point. The purpose of cooling is to significantly extend the storage stability of the photoinitiator, avoid thermal initiation side reactions at higher temperatures, and reduce the tendency of dispersed components to re-aggregate due to excessive Brownian motion. Under light-protected conditions, a photocrosslinking agent (epoxy acrylate) and a compound photoinitiator are added. As a medium-viscosity oligomer, epoxy acrylate can be rapidly dissolved in the S3 mixture at 35°C with continuous stirring. The stirring and mixing at this stage aims to achieve a uniform distribution of the photoinitiator and crosslinking agent at the molecular level, which is a prerequisite for ensuring a uniform and thorough UV curing reaction and avoiding insufficient curing or excessive crosslinking in certain areas.

[0039] Under light-protected stirring at 35°C, significant chemical crosslinking reactions have not yet begun. However, the epoxy groups in the photocrosslinking agent molecules and the carboxyl groups already present in the system (from the reaction products of fluorinated cyclic olefin-maleic anhydride copolymer and hydroxyl-terminated fluorinated polyether) may undergo an extremely slow thermally initiated acid-epoxy ring-opening reaction. However, this reaction rate is extremely low under low temperature, catalyst-free, and light-protected conditions, and its effect on the system viscosity is negligible. More importantly, the photoinitiators benzophenone (BP) and 2-isopropylthioxanthraquinone (ITX) dissolve and reach dynamic equilibrium under these conditions. BP tends to be distributed mainly in the surface region of the slurry because it needs to abstract hydrogen atoms from tertiary amine (or ether) co-initiators to generate active free radicals, making it more suitable for surface curing. ITX, due to its molecular structure characteristics, has high absorption efficiency for long-wave UV and can directly initiate polymerization after photolysis, enabling it to penetrate the slurry for deep curing. The combination of the two lays the chemical foundation for simultaneous and uniform curing of the "surface-deep" layers.

[0040] The subsequent high-vacuum settling is equivalent to a physical purification process. The microbubbles dissolved in the slurry expand, merge and escape under negative pressure, and are completely eliminated, preventing residual bubbles from forming pinhole defects in the cured adhesive film, which would become stress concentration points, electrolyte penetration channels and sources of early failure.

[0041] This process produces a homogeneous, bubble-free, and viscosity-stable final adhesive slurry. It is in a "photosensitive, ready-to-trigger" state, and once exposed to UV light, it can quickly and uniformly cure into a dense, high-performance adhesive film, ensuring the integrity, sealing, and long-term reliability of the adhesive layer.

[0042] S6. Coating and Packaging:

[0043] Under light-protected conditions, use a comma-shaped doctor blade coater to evenly coat the adhesive slurry onto the release film, controlling the wet film thickness to 40-60μm. After winding, use aluminum-plastic composite film for vacuum packaging and store in the dark.

[0044] Light protection is maintained throughout the coating, winding, and packaging processes to prevent premature activation of the photoinitiator, which could lead to prepolymerization and gelation of the slurry. This ensures the processability of subsequent UV curing. The comma-shaped doctor blade coater uses gap control and shear leveling to coat the slurry into a uniform 40-60μm wet film. The low surface energy of the release film prevents adhesion and ensures the flatness of the film. This thickness balances complete curing and cost. Constant tension during winding prevents deformation of the wet film. Vacuum packaging of the aluminum-plastic composite film isolates light, oxygen, and moisture, preventing the decay of active groups or hydrolysis of acid anhydrides. This ensures the stability of the slurry's performance during storage and provides consistent raw materials for subsequent large-scale processing.

[0045] Preferably, the preparation steps of modified nano-zirconia are as follows:

[0046] The nano-zirconia powder was dispersed in an ethanol aqueous solution and ultrasonically dispersed. The hydrolysate of silane coupling agent KH-570 was slowly added dropwise. After the addition was completed, the system was heated to 70°C and stirred at a constant speed for 12 hours. After centrifugation, the mixture was washed three times with anhydrous ethanol and vacuum dried to obtain modified nano-zirconia powder with methacrylate groups grafted on its surface.

[0047] Preferably, the fluorine content of the fluorinated cyclic olefin-maleic anhydride copolymer is 7-9% by mass, the content of maleic anhydride structural units is 10-13 mol%, and the terminal hydroxyl fluorinated polyether has a fluorine content of 8-10% by mass and a hydroxyl value of 60-80 mg KOH / g.

[0048] Preferably, after adding other additives, the premixed melt is first dispersed at a low speed of 800 rpm, and then dispersed at a high speed of 2000 rpm. The particle size of the adhesive slurry is D90≤50nm, and the viscosity at 25℃ is 20000-25000mPa·s.

[0049] Compared with the prior art, the beneficial effects of the present invention are:

[0050] 1. By employing a synergistic approach of fluorinated ternary copolymerization and covalent anchoring of fluorinated compatibilizers, combined with the mechanism of alternating free radical copolymerization to construct a rigid fluorinated skeleton and anhydride-hydroxyl ring-opening esterification, the core contradiction of high-temperature residue and interfacial adhesion is resolved. Norbornene provides a high-temperature resistant main chain, hexafluorobutyl acrylate introduces fluorine to inhibit carbonization, and maleic anhydride and hydroxyl-terminated fluorinated polyether undergo ring-opening esterification. The compatibilizer is covalently anchored to avoid phase separation, and the interfacial bonding of aluminum tabs is strengthened. This achieves a residue of ≤0.2% after 500 cycles at 150℃ and a peel strength of ≥9.0MPa, breaking through the performance trade-off limitations of traditional physical blending.

[0051] 2. A dual stabilization method using modified nano-zirconia and fluorinated hyperbranched polyester, combined with the related mechanisms of similar-to-similarity wetting and physical encapsulation-chemical anchoring, solves the problems of nanofiller agglomeration and additive migration. The methacrylate groups of modified nano-zirconia are compatible with the system, and the fluorinated hyperbranched polyester is dispersed through fluorine-fluorine interaction. Its hyperbranched structure physically encapsulates the filler, and the β-diketone groups are chemically anchored to zirconium ions, simultaneously achieving metal chelation and anti-degradation. The slurry particle size D90≤50nm and no long-term sedimentation.

[0052] 3. A step-by-step temperature control method is adopted to construct a photocrosslinking system. Combined with low-temperature dispersion to prevent prepolymerization and a gradient curing mechanism of compound initiators, the problems of storage stability and uneven curing are solved. After premixing at 60℃, the temperature is lowered to 35℃ to introduce the crosslinking agent, avoiding the thermal activation of the photoinitiator. Benzoyl (surface curing) and 2-isopropylthioxanthone (deep curing) are compounded and combined with high vacuum degassing to achieve stable viscosity of the slurry after 72 hours of light-proof storage and no defects after curing, solving the pain point of "surface skin formation and deep uncured" in traditional photocuring.

[0053] 4. A one-step functionalization method using fluorinated hyperbranched polyester is adopted, combined with the introduction of chelating groups through transesterification and the mechanism of fluorinated end groups through epoxy ring-opening, which solves the problem of poor compatibility of stabilizers. Ethyl acetoacetate is transesterified with hydroxyl-terminated hyperbranched polyester to introduce β-diketone chelating groups, and then fluorinated end groups are introduced through ring-opening with perfluorooctyl propylene oxide. The fluorinated end groups improve the compatibility with the host. The physical migration barrier of the hyperbranched structure and the chemical fixation of the chelating groups are combined to improve the migration resistance by 60%, avoiding the migration defects of traditional stabilizers. Attached Figure Description

[0054] Figure 1 This invention provides a process flow for preparing low-residue tab adhesive film bonding materials. Detailed Implementation

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0056] Example 1: Preparation method of low residual lithium battery positive electrode tab adhesive film:

[0057] S1. Preparation of fluorinated cyclic olefin-maleic anhydride copolymer:

[0058] Under dry nitrogen protection, norbornene, hexafluorobutyl acrylate and maleic anhydride were added to a reaction vessel in a mass ratio of 50:40:10 with 3 times the total mass of dehydrated toluene. The temperature was raised to 85°C, benzoyl peroxide was added, and the reaction was carried out for 6 hours. The mixture was poured into an ethanol / water mixed solvent, filtered, washed with ethanol, and dried to obtain a fluorinated cyclic olefin-maleic anhydride copolymer.

[0059] S2. Preparation of hyperbranched polyesters with fluorinated alkane-modified end groups:

[0060] Under nitrogen protection, hydroxyl-terminated hyperbranched polyester and N,N-dimethylformamide were added to a reaction vessel at a mass ratio of 1:3, stirred and dissolved, heated to 80°C, and 7% (by mass) of ethyl acetoacetate was slowly added dropwise. The reaction was carried out for 7 hours, and then 4% (by mass) of perfluorooctyl propylene oxide and 0.1% (by mass) of tetrabutylammonium bromide were added. The reaction was continued at 70°C for 10 hours. The product was precipitated with ice-cold ether, filtered, washed three times with ethanol, and dried under vacuum for 12 hours to obtain a hyperbranched polyester product with fluoroalkane-modified terminal groups.

[0061] S3. Premixing:

[0062] Fluorinated cyclic olefin-maleic anhydride copolymer, hydroxyl-terminated fluorinated polyether and trimethylolpropane triacrylate were added to a planetary mixer in a mass ratio of 45:15:12 and stirred for 60 min at 60°C and a vacuum of -0.095 MPa to obtain a uniform, transparent or semi-transparent viscous premixed melt.

[0063] S4. Packing dispersion:

[0064] Modified nano-zirconia, hyperbranched polyester with fluoroalkane-modified end groups, and polyether-modified polydimethylsiloxane were added sequentially to the premixed melt in a mass ratio of 5:3:1.5. The mixture was then stirred and dispersed at low speed for 15 min at 60 °C and under vacuum of -0.095 MPa, followed by high speed dispersion for 40 min.

[0065] S5. Introduction and degassing of the crosslinking system:

[0066] The mixture was cooled to 35°C, and under light-protected conditions, epoxy acrylate and photoinitiator were added in a mass ratio of 8:2. The mixture was stirred for 25 minutes and then allowed to stand under a high vacuum of -0.098MPa for 30 minutes to degas, thus obtaining the final adhesive slurry.

[0067] S6. Coating and Packaging:

[0068] Under light-protected conditions, use a comma-shaped doctor blade coater to evenly coat the adhesive slurry onto the release film, controlling the wet film thickness to 50μm. After winding, use aluminum-plastic composite film for vacuum packaging and store in the dark.

[0069] Example 2: Preparation method of low residual lithium battery positive electrode tab adhesive film:

[0070] S1. Preparation of fluorinated cyclic olefin-maleic anhydride copolymer:

[0071] Under dry nitrogen protection, norbornene, hexafluorobutyl acrylate and maleic anhydride were added to a reaction vessel in a mass ratio of 50:40:10 with 3 times the total mass of dehydrated toluene. The temperature was raised to 85°C, benzoyl peroxide was added, and the reaction was carried out for 6 hours. The mixture was poured into an ethanol / water mixed solvent, filtered, washed with ethanol, and dried to obtain a fluorinated cyclic olefin-maleic anhydride copolymer.

[0072] S2. Preparation of hyperbranched polyesters with fluorinated alkane-modified end groups:

[0073] Under nitrogen protection, hydroxyl-terminated hyperbranched polyester and N,N-dimethylformamide were added to a reaction vessel at a mass ratio of 1:3, stirred and dissolved, heated to 80°C, and 7% (by mass) of ethyl acetoacetate was slowly added dropwise. The reaction was carried out for 7 hours, and then 4% (by mass) of perfluorooctyl propylene oxide and 0.1% (by mass) of tetrabutylammonium bromide were added. The reaction was continued at 70°C for 10 hours. The product was precipitated with ice-cold ether, filtered, washed three times with ethanol, and dried under vacuum for 12 hours to obtain a hyperbranched polyester product with fluoroalkane-modified terminal groups.

[0074] S3. Premixing:

[0075] Fluorinated cyclic olefin-maleic anhydride copolymer, hydroxyl-terminated fluorinated polyether and trimethylolpropane triacrylate were added to a planetary mixer in a mass ratio of 55:15:12 and stirred for 60 min at 60°C and a vacuum of -0.095 MPa to obtain a uniform, transparent or semi-transparent viscous premixed melt.

[0076] S4. Packing dispersion:

[0077] Modified nano-zirconia, hyperbranched polyester with fluoroalkane-modified end groups, and polyether-modified polydimethylsiloxane were added sequentially to the premixed melt in a mass ratio of 5:3:1.5. The mixture was then stirred and dispersed at low speed for 15 min at 60 °C and under vacuum of -0.095 MPa, followed by high speed dispersion for 40 min.

[0078] S5. Introduction and degassing of the crosslinking system:

[0079] The mixture was cooled to 35°C, and under light-protected conditions, epoxy acrylate and photoinitiator were added in a mass ratio of 8:2. The mixture was stirred for 25 minutes and then allowed to stand under a high vacuum of -0.098MPa for 30 minutes to degas, thus obtaining the final adhesive slurry.

[0080] S6. Coating and Packaging:

[0081] Under light-protected conditions, use a comma-shaped doctor blade coater to evenly coat the adhesive slurry onto the release film, controlling the wet film thickness to 50μm. After winding, use aluminum-plastic composite film for vacuum packaging and store in the dark.

[0082] Example 3: Preparation method of low residual lithium battery positive electrode tab adhesive film:

[0083] S1. Preparation of fluorinated cyclic olefin-maleic anhydride copolymer:

[0084] Under dry nitrogen protection, norbornene, hexafluorobutyl acrylate and maleic anhydride were added to a reaction vessel in a mass ratio of 50:40:10 with 3 times the total mass of dehydrated toluene. The temperature was raised to 85°C, benzoyl peroxide was added, and the reaction was carried out for 6 hours. The mixture was poured into an ethanol / water mixed solvent, filtered, washed with ethanol, and dried to obtain a fluorinated cyclic olefin-maleic anhydride copolymer.

[0085] S2. Preparation of hyperbranched polyesters with fluorinated alkane-modified end groups:

[0086] Under nitrogen protection, hydroxyl-terminated hyperbranched polyester and N,N-dimethylformamide were added to a reaction vessel at a mass ratio of 1:3, stirred and dissolved, heated to 80°C, and 7% (by mass) of ethyl acetoacetate was slowly added dropwise. The reaction was carried out for 7 hours, and then 4% (by mass) of perfluorooctyl propylene oxide and 0.1% (by mass) of tetrabutylammonium bromide were added. The reaction was continued at 70°C for 10 hours. The product was precipitated with ice-cold ether, filtered, washed three times with ethanol, and dried under vacuum for 12 hours to obtain a hyperbranched polyester product with fluoroalkane-modified terminal groups.

[0087] S3. Premixing:

[0088] Fluorinated cyclic olefin-maleic anhydride copolymer, hydroxyl-terminated fluorinated polyether and trimethylolpropane triacrylate were added to a planetary mixer in a mass ratio of 50:15:12 and stirred for 60 min at 60°C and a vacuum of -0.095 MPa to obtain a uniform, transparent or semi-transparent viscous premixed melt.

[0089] S4. Packing dispersion:

[0090] Modified nano-zirconia, hyperbranched polyester with fluoroalkane-modified end groups, and polyether-modified polydimethylsiloxane were added sequentially to the premixed melt in a mass ratio of 5:3:1.5. The mixture was then stirred and dispersed at low speed for 15 min at 60 °C and under vacuum of -0.095 MPa, followed by high speed dispersion for 40 min.

[0091] S5. Introduction and degassing of the crosslinking system:

[0092] The mixture was cooled to 35°C, and under light-protected conditions, epoxy acrylate and photoinitiator were added in a mass ratio of 8:2. The mixture was stirred for 25 minutes and then allowed to stand under a high vacuum of -0.098MPa for 30 minutes to degas, thus obtaining the final adhesive slurry.

[0093] S6. Coating and Packaging:

[0094] Under light-protected conditions, use a comma-shaped doctor blade coater to evenly coat the adhesive slurry onto the release film, controlling the wet film thickness to 50μm. After winding, use aluminum-plastic composite film for vacuum packaging and store in the dark.

[0095] Comparative Example 1:

[0096] Compared with Example 3, the mass ratio of fluorinated cyclic olefin-maleic anhydride copolymer, hydroxyl-terminated fluorinated polyether and trimethylolpropane triacrylate in Comparative Example 1 was 60:15:12.

[0097] Comparative Example 2:

[0098] Compared with Example 3, in Comparative Example 2, the hyperbranched polyester was not subjected to a fluorination step, while the other components and processes remained unchanged.

[0099] Comparative Example 3:

[0100] Compared with Example 3, Comparative Example 3 replaced the hydroxyl-terminated fluorinated polyether with a common fluorinated compatibilizer, contained no other components, and the process remained unchanged.

[0101] Comparative Example 4:

[0102] Compared with Example 3, in Comparative Example 4, the hydroxyl-terminated hyperbranched polyester was replaced with a traditional benzotriazole stabilizer, while other components and the process remained unchanged.

[0103] Comparative Example 5:

[0104] Compared with Example 3, in Comparative Example 5, the complex photoinitiator was replaced with a single benzophenone, while the other components and processes remained unchanged.

[0105] Performance testing:

[0106] According to GB / T 2792-2014 "Test Method for 180° Peel Strength of Adhesive Tapes", GB / T 2793-1995 "Determination of Non-volatile Content in Adhesives", GB / T 14074-2017 "Test Methods for Adhesives and Resins for Wood Industry", GB / T1040.3-2006 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets", GB / T 2411-2008 "Shore Hardness Test Method for Plastics and Hard Rubber", GB / T The adhesive materials prepared in the above examples and comparative examples were tested according to the standard tests in GB / T 2423.22-2012 "Environmental Testing Part 2: Test Methods Test N: Temperature Change", including 180° aluminum foil peel strength, residual amount after high temperature cycling, adhesive strength retention rate after electrolyte immersion, tensile strength and elongation at break of adhesive film, Shore hardness of adhesive film, viscosity change rate, and resistance to high and low temperature cycling.

[0107] The physicochemical properties of the adhesive materials prepared in the examples and comparative examples were tested according to the above test methods. The test results are shown in Table 1 below:

[0108] Table 1. Physical and chemical performance test data

[0109]

[0110] Following the above testing methods, the functional performance of the adhesive materials prepared in the examples and comparative examples was tested, and the test results are shown in Table 2 below:

[0111] Table 2 Functional Performance Test Data

[0112]

[0113] Data Analysis:

[0114] Figure 1 The present invention discloses a process for preparing low-residue tab adhesive film. The overall process is as follows: First, a self-made fluorinated cyclic olefin-maleic anhydride copolymer, a reactive compatibilizer, and an active diluent are premixed. Then, modified nano-zirconia, a self-made end-group fluorinated modified hyperbranched polyester, and a dispersant are added to the premix to complete the filler dispersion. Next, a crosslinking agent and a photoinitiator are added while the mixture is cooled and protected from light. After mixing, the mixture is degassed under high vacuum to obtain an adhesive slurry. Finally, the slurry is coated onto a release film using a comma-shaped scraper while protected from light. After controlling the wet film thickness, the film is rolled up, vacuum-packed with an aluminum-plastic composite film, and stored in the dark.

[0115] In Example 1, the proportion of the main prepolymer in the adhesive slurry was low, and its overall performance was slightly inferior to the reference sample. When the proportion of the main prepolymer was low, although the system had good dispersibility, its supporting role as a skeleton was slightly weaker. According to the performance test data in Tables 1 and 2, the interfacial bonding strength, mechanical strength, and environmental stability all decreased slightly, demonstrating the fundamental supporting role of the main skeleton content in the core performance of the material.

[0116] Example 2, as an example of a high proportion of the main prepolymer, showed performance close to the benchmark but not surpassing it. The increased proportion of the main prepolymer enhanced the material's rigidity, improving tensile strength and hardness. However, the excessively high proportion of the main prepolymer increased the system viscosity and slightly reduced the dispersion efficiency of the reactive diluent and compatibilizer, resulting in a slight decrease in toughness indicators such as elongation at break. This reflects that a suitable ratio between the main prepolymer and other components is needed to achieve performance balance.

[0117] In Example 3, the main prepolymer had the optimal proportion in the system, exhibiting the best overall performance. The moderate proportion of the main prepolymer ensured both the rigid support of the skeleton and its resistance to high-temperature residues, while also providing a good dispersion environment for components such as compatibilizers and reactive diluents. This allowed the covalent anchoring and fluorine synergistic effects to be fully realized, and key indicators such as interfacial adhesion, electrolyte resistance, and resistance to high and low temperature cycling all reached their optimal levels, verifying that the synergistic effect of each component was maximized under this ratio.

[0118] In Comparative Example 1, the excessive prepolymer content resulted in significantly inferior performance compared to the reference sample. The high prepolymer content led to a substantial increase in system viscosity. The three-dimensional shear force of the planetary mixer made it difficult to achieve molecular-level dispersion of the components. The compatibilizer could not be uniformly anchored to the main framework, and the nanofillers were prone to localized agglomeration. This not only significantly reduced interfacial bonding strength but also increased localized carbonization residues during high-temperature cycling due to uneven dispersion. Furthermore, the performance retention rate after high and low temperature cycling was significantly reduced, highlighting the destructive effect of an excessive prepolymer content on dispersibility and synergistic effects.

[0119] The core variable in Comparative Example 1 is that the proportion of the main prepolymer exceeded the upper limit of the optimal range, and this adjustment directly triggered a chain reaction of performance changes. Data shows that key indicators such as interfacial bonding strength and high / low temperature cycling stability all declined significantly, while the residual amount after high-temperature cycling also increased markedly. Upon closer examination, the excessively high proportion of the main prepolymer caused the system viscosity to far exceed the suitable range. The three-dimensional shear force of the planetary mixer could not effectively break the molecular chain entanglement, making it difficult for the compatibilizer to be uniformly anchored to the main framework. The nanofillers also formed localized agglomerations due to increased dispersion resistance. This uneven dispersion not only weakened the synergistic effect of interfacial bonding but also caused intensified localized carbonization at high temperatures, ultimately resulting in a comprehensive decline in various properties, confirming the importance of strictly controlling the proportion of the main prepolymer within a reasonable range.

[0120] Focusing on Comparative Example 2, its core difference from the baseline sample is that the hyperbranched polyester was not fluorinated, a functional deficiency directly reflected in the performance data. The most prominent change is a significant decline in strength retention and high / low temperature cycling resistance after electrolyte immersion, along with a certain degree of decrease in interfacial adhesion strength. The fundamental reason is that, without fluorinated end groups, the compatibility of the hyperbranched polyester with the fluorinated main component and fluorinated compatibilizer in the system is greatly reduced, making it impossible to achieve uniform dispersion at the molecular level. Consequently, its physical encapsulation and stabilizing effect on the nanofiller is weakened. Simultaneously, the hydrophobic and electrolyte-resistant properties imparted by fluorine are lost, making the film more susceptible to corrosion during electrolyte immersion and high / low temperature cycling. This further verifies the dual crucial role of fluorination modification in compatibility and functional synergy.

[0121] Comparative Example 3 replaced the hydroxyl-terminated fluorinated polyether with a common fluorinated compatibilizer. This replacement led to the most significant performance shortcoming—a substantial decrease in interfacial bonding strength, with the most severe performance degradation occurring after electrolyte immersion and high / low temperature cycling. From a mechanistic perspective, the common fluorinated compatibilizer lacks active hydroxyl groups and cannot undergo ring-opening esterification with the anhydride groups in the main prepolymer. It can only rely on physical mixing and dispersion in the system, resulting in extremely weak bonding with the main skeleton. More importantly, the lack of coordination and hydrogen bonding between hydroxyl groups and the alumina surface of the aluminum electrode leads to inherently weak interfacial bonding, making it prone to delamination under harsh conditions. This fully demonstrates the irreplaceable role of hydroxyl-terminated fluorinated polyether in strengthening interfacial bonding through covalent anchoring.

[0122] Comparative Example 4, which replaced the fluorinated hyperbranched polyester with a traditional benzotriazole stabilizer, showed performance data indicating increased high-temperature residue and decreased resistance to electrolytes and high / low temperature stability. This change stems from the limited functionality of traditional stabilizers: on the one hand, they have poor compatibility with fluorinated systems, and uneven dispersion leads to reduced anti-migration effects; on the other hand, they lack the physical migration-blocking effect of hyperbranched structures and the chemical chelating function of β-diketone groups, failing to effectively inhibit small molecule migration and metal ion catalytic degradation. Consequently, under long-term high-temperature and electrolyte immersion, the film exhibits increased small molecule residue and decreased structural stability, highlighting the multifunctional integrated advantages of fluorinated hyperbranched polyesters, which combine physical migration blocking, chemical chelation, and compatibility.

[0123] Comparative Example 5, where the compound photoinitiator was replaced with single benzophenone, showed the most noticeable change in performance: an increased rate of viscosity change during slurry storage, a significant decrease in strength retention after high and low temperature cycling, and a slight decrease in interfacial bond strength. The core issue lies in curing uniformity: single benzophenone has limited curing penetration, ensuring only sufficient curing of the surface layer of the film, while the cross-linking density in the deeper layers is insufficient, resulting in a heterogeneous structure of "hard surface and soft inner layers." This structure not only leads to slow migration of inner layer components during storage, increasing viscosity fluctuations, but also causes performance degradation during high and low temperature cycling due to uneven internal and external stresses, strongly demonstrating the necessity of compound photoinitiators to achieve simultaneous and uniform curing of the "surface-deep" layers.

[0124] Based on all the embodiments and comparative examples, it can be seen that the high performance of low-residue lithium battery cathode tab adhesive film depends on the precise matching of component ratios, the structural modification and precise selection of functional components, and the integrated synergy of "structural design - component synergy - process adaptation". The proportion of the main prepolymer needs to be controlled within a reasonable range. Modified functional components such as fluorinated hyperbranched polyester, hydroxyl-terminated fluorinated polyether, and compounded photoinitiators are irreplaceable. Only the combined effect of the three can solve the core pain points of traditional materials and achieve comprehensive performance of low residue, high adhesion, and long-term stability.

[0125] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-residue lithium battery positive electrode tab adhesive film bonding material, characterized in that, The components include the following parts by weight: Main prepolymer: 45-55 parts, is a fluorinated cyclic olefin-maleic anhydride copolymer, and the preparation method of the fluorinated cyclic olefin-maleic anhydride copolymer is as follows: Under dry nitrogen protection, norbornene, hexafluorobutyl acrylate and maleic anhydride and dehydrated toluene were added to a reaction vessel, heated to 85°C, benzoyl peroxide was added, and the reaction was carried out for 6 hours. The mixture was poured into an ethanol / water mixed solvent, filtered, washed with ethanol, and dried to obtain a fluorinated cyclic olefin-maleic anhydride copolymer. Reactive compatibilizer: 12-18 parts, hydroxyl-terminated fluorinated polyether; Photocrosslinking agent: 6-10 parts, which is epoxy acrylate; Photoinitiator: 1.5-2.5 parts, a compound composed of benzophenone and 2-isopropylthioxanthraquinone in a mass ratio of 3:1; Nano-active filler: 4-6 parts, which is modified nano-zirconia with surface grafted methacrylate groups. The preparation steps of the modified nano-zirconia are as follows: The nano-zirconia powder was dispersed in an ethanol aqueous solution and ultrasonically dispersed. The hydrolysate of silane coupling agent KH-570 was slowly added dropwise. After the addition was completed, the system was heated to 70℃ and stirred at a constant speed for 12 hours. After centrifugation, the nano-zirconia powder was washed three times with anhydrous ethanol and vacuum dried to obtain modified nano-zirconia powder with methacrylate groups grafted on its surface. Anti-migration stabilizer: 2.5-3.5 parts, which is a hyperbranched polyester with fluoroalkane-modified end groups. The preparation steps of the hyperbranched polyester with fluoroalkane-modified end groups are as follows: Under nitrogen protection, trimethylolpropane, hyperbranched polyester prepolymer, and 2,2-dimethylolpropionic acid were added to a reactor. Using p-toluenesulfonic acid as a catalyst, a melt polycondensation reaction was carried out at 140-150℃ for 4-6 hours. The temperature was then lowered to 80℃, N,N-dimethylformamide was added, and ethyl acetoacetate was added dropwise. The reaction was carried out for 6-8 hours, and perfluorooctyl propylene oxide was added. Under the catalysis of tetrabutylammonium bromide, the reaction was carried out at 70-75℃ for 10-12 hours. The precipitate was collected, filtered, washed three times with ethanol, and dried under vacuum. Dispersant: 1-2 parts, which is polyether-modified polydimethylsiloxane; Reactive diluent: 10-15 parts, which is trimethylolpropane triacrylate.

2. The low-residue lithium battery positive electrode tab adhesive film bonding material according to claim 1, characterized in that, The fluorinated cyclic olefin-maleic anhydride copolymer has a fluorine content of 7-9% by mass and a maleic anhydride structural unit content of 10-13 mol%. The terminal hydroxyl fluorinated polyether has a fluorine content of 8-10% by mass and a hydroxyl value of 60-80 mg KOH / g.

3. A method for preparing a low-residue lithium battery positive electrode tab adhesive film as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Premixed: Fluorinated cyclic olefin-maleic anhydride copolymer, hydroxyl-terminated fluorinated polyether and trimethylolpropane triacrylate were added to a planetary mixer and stirred for 60 min at 60 °C and a vacuum of -0.095 MPa to obtain a uniform, transparent or semi-transparent viscous premixed melt. S2. Packing dispersion: Modified nano-zirconia, hyperbranched polyester with fluoroalkane-modified end groups, and polyether-modified polydimethylsiloxane were added sequentially to the premixed melt. The mixture was then stirred and dispersed at low speed for 15 min under 60℃ and -0.095MPa vacuum conditions, followed by high-speed dispersion for 40 min. S3. Introduction and degassing of the crosslinking system: The mixture was cooled to 35°C, and epoxy acrylate and photoinitiator were added under light-protected conditions. The mixture was stirred for 25 minutes and then allowed to stand under a high vacuum of -0.098MPa for 30 minutes to degas, thus obtaining the final adhesive slurry. S4. Coating and Packaging: Under light-protected conditions, use a comma-shaped doctor blade coater to evenly coat the adhesive slurry onto the release film, controlling the wet film thickness to 40-60μm. After winding, use aluminum-plastic composite film for vacuum packaging and store in the dark.

4. The method for preparing a low-residue lithium battery positive electrode tab adhesive film as described in claim 3, characterized in that, In the S2 premixed melt, after adding other additives, it is first dispersed at a low speed of 800 rpm, and then the speed is increased to 2000 rpm for high-speed dispersion.

5. The method for preparing a low-residue lithium battery positive electrode tab adhesive film as described in claim 3, characterized in that, The adhesive slurry in S3 has a particle size D90≤50nm and a viscosity of 20000-25000mPa·s at 25℃.

6. An adhesive layer for an electrode film, characterized in that, It is prepared by coating and curing the adhesive slurry according to claim 3.

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